Since Hammerschmidt discovered in 1934 that gas hydrates would block gas pipelines, research for the prevention of hydrate formation and agglomeration has become an important matter. Gas hydrates can be easily formed during the transportation of oil and gas in pipelines when the appropriate conditions are present. Water content, low temperatures, and elevated pressure are required for the formation of gas hydrates. The formation of gas hydrates often result on lost oil production, pipeline damage, and safety hazards to field workers. Modern oil and gas technologies commonly operate under severe conditions during the course of oil recovery and production; for instance, high pumping speed, high pressure in the pipelines, extended length of pipelines, and low temperature of the oil and gas flowing through the pipelines. These conditions are particularly favorable for the formation of gas hydrates, which can be particularly hazardous for oil productions offshore or for locations with cold climates.
Gas hydrates are ice-like solids that are formed from small nonpolar molecules and water at lower temperatures and at increased pressures. Under these conditions, the water molecules can form cage-like structures around these small nonpolar molecules (typically dissolved gases such as carbon dioxide, hydrogen sulfide, methane, ethane, propane, butane and iso-butane), creating a type of host-guest interaction also known as a clathrate or clathrate hydrate. The specific architecture of this cage structure can be one of several types (called type 1, type 2, type H), depending on the identity of the guest molecules. However, once formed, these crystalline cage structures tend to settle out from the solution and accumulate into large solid masses that can travel by oil and gas transporting pipelines, and potentially block or damage the pipelines and/or related equipment. The damage resulting from a blockage can be very costly from an equipment repair standpoint, as well as from the loss of production, and finally the resultant environmental impact.
The industry uses a number of methods to prevent such blockages such as thermodynamic hydrate inhibitors (THI), anti-agglomerants (AA), and kinetic hydrate inhibitors (KHI). The amount of chemical needed to prevent blockages varies widely depending upon the type of inhibitor that is employed. Thermodynamic hydrate inhibitors are substances that can reduce the temperature at which the hydrates form at a given pressure and water content and are typically used at very high concentrations (regularly dosed as high as 50% based on water content—glycol is often used in amounts as high as 100% of the weight of the produced water). Therefore, there is a substantial cost associated with the transportation and storage of large quantities of these solvents.
A more cost-effective alternative is the use of LDHIs, as they generally require less that 2% dose to inhibit the nucleation or growth of gas hydrates. There are two general types of LDHIs, kinetic hydrate inhibitors (KHIs) and anti-agglomerants (AAs), which are both typically used at much lower concentrations (0.3-0.5% active concentration). KHIs work by delaying the growth of gas hydrate crystals and as anti-nucleators. AAs allow the hydrates to form but they prevent them from agglomerating and subsequent accumulation into larger masses capable of causing plugs. An AA enables gas hydrates to form but in the shape of fluid slurry dispersed in the liquid hydrocarbon phase. In general, the water cut should be below 50% otherwise the slurry become too viscous to transport.
There is therefore an ongoing need for new and effective methods of inhibiting the formation of hydrate agglomerates, particularly those that are capable of operating under higher water-cuts.